Shredded cellulose pulp adapted for nitration and the process of making it



Sept. 27, 1932. M. o. scHuR E'r Al. 1,880,052

SHREDDED CELLULOSE PULP ADAPTED FOR NITRATION AND THE PROCESS OF MAKING IT Filed Sept. 2l. 1929 4 egizi v.

affzagfw wie@ a@ Patented Sept. 27,4 1932 UNITED STATES laxiuauar OFFICE MILTON O. SCHUR AND BENJAMIN G.

T0 BROWN COMPANY, OF BERLIN,

HOOS, 0F BERLIN, NEW HAMPSHIRE, ASSIGNORS NEW HAMPSHIRE, A CORPORATION OF MAINE snannnnn cnLLULosE PULP Anarrnn ron NmnA'rroN-AND THE rnocEss or e MAKING r1' l Application led September 21, 1929. Serial No. 394,370.

This invention relates to the conditioning of cellulose ber for conversion'into cellulose derivatives, being more particularly concerned with the conditioning of wood pulps for conversion into cellulose esters such as the cellulose nitrates.

In order to realize good results when using cellulose ber such as wood pulp as a raw -material for conversion into cellulose derivatives such as the cellulose nitrates, it is necessary that the ber be in such condition that the mixed nitrating acids will penetrate uniiiormly into and react smoothlyand uniformly therewith.' The desired condition of the bers may be obtained by preparing a tissue or waterleai` paper therefrom and then disintegrating the paper into flakes presenting a large area of contact with the mixed nitating acids. This method of conditioningthe ber, however, is comparatively ex-` pensive, so that it is sometimes the practice to pass wood pulp in bulk Jforno through teasing or picking machines to produce a fluffy, absorbent mass, much like cotton batting. For the preparation of some cellulose derivatives such as cellulose acetate, this may be good practice, as in such case directacetylation only takes place, but may constitute improper practice in the preparation'oi nitrocelluloses where secondary reactions may accompany the main one oi? nitration. For instance, in the preparation of the lower nitrocelluloses of, say, less than 11.5% nitrogen content, secondary reactions of a hydrolytic nature may be sufficiently serious to result in low yields and an inferior product. 'These secondary reactions are evidently encouraged when the cellulose ber is uiied as hereinbefore described. Itis our theory that as the mixed nitrating acids react with cellulose ber, they become weaker in nitric acid and richer in water content, tending to hydrolyze the bers rather than to nitrate them. In order to realize a high yield of good product, it is apparently necessary that the mixed acids .be a'orded ample opportunity to diffuse into and through the bers from the main body of acid, and further that the Water generated in the bers be aorded ample opportunity to di'use into the main body of acid. With the bers in a highly absorptive condition, nitration of the bers evidently takes place so rapidly that there is insuiiicient time for the desired diffusive action to take place to. ensure the proper composition of mixed nitrating acids in the bers. Various expedients may be adopted to check the rate of reaction between the-ber and the mixed nitratirig acidsto-permit the desired diffusive actions to take place. For instance, as disclosed and claimed in our application Serial No. 336,633, led January 31, 1929, the bers may be coated vwith a trace of acid-repellent material, such as parain wax, which serves to retard the nitrating reaction.

We have now discovered that if cellulose ber such as wood pulp is nely shredded under predetermined conditions of moisture content and then permitted to dry, it takes on a physical condition highly satisfactory for nitration. The precise moisture content at which optimum results with regard to yield and quality may vary, depending upon such factors as the type of shredding machine employed. As far as results at present indicate, the ul should preferably contain about 40% to ilOi bone-dry cellulose ber while being Shredded. Apparently if the pulp is appreciably dryer during shredding, brous dust is generated and a too highly absorbant product, which reacts too rapidly, is produced. It, on the other hand, the pulp 1s appreciably wetter during shredding, difficulty is experienced in obtaining the desired degree and uniformity of shredding, with the result that hard, compact lumps which are non-uniformly reacted upon, may be present in the shredded product. On the accompanying drawing, the yield of nitrated product obtained from of nitrocellulose are obtained shredded pulp is plotted against the bonedry cellulose content during shredding. It is to be noted that the yield curve reaches a maximum value at the region of about 40% to bone-dry cellulose content, at which content we prefer to carry out our shredding operation.

We have further observed that the improved results hereinbefore noted are obtained irrespective of Whether the fiber is initially suiiiciently wet or must be preliminary moistened, as by steaming or wetting with water. In practice pulp must be stored in dry condition in order to avoid mouldingl or spontaneous decomposition. Inasmuch as nitration is usually carried out in comparatively small batches, the nitrocellulose manufacturer or other converter may enjoy the beneits of our discovery by storing the pulp in dry condition, taking it as needed from storage, and imparting thereto the moisture content desired for shredding immediately before nitration. If the nitration mill is operated simultaneously with a pulp mill, the pulp may be taken immediately after processing in the pulp mill as a suspension in water and delivered into a wet or cylinder machine equipped with a couch rollwhich exerts heavy pressure on the web so that the laps stripped from the make-up roll of the machine are of low water content and need be dewatered only under the action of hydraulic presses to produce the moisture content desired for shredding. If desired, the pulp may be sheeted on a. paper machine into Ya comparatively thick, porous sheet, which may be dewatered to the desired moisture content bythe action of heavy press rolls and/or dryers, whereupon the` continuous sheet coming from the machine may be linely shredded by passing one or moreV times through teasing or picking machines, or under a cylindrical wire brush rotating rapidly in Contact with a bed-plate. Or the sheeted or bulk fiber may becharged into a closed container provided with a dull-edged blade agitator, which is caused to rotate rapidly in the container while relative motion between the container and agitator is produced in order to ensure uniform andcomplete shredding. The shredded fiber may be delivered onto a conveyor moving through a tunneldryer through which a stream of hot air is passed counter-current to the direction of travel of the conveyor.

The dry, shredded fiber may be nitrated in baths of mixed nitrating acids of various compositions, depending upon the nitrogen content desired in the product. When producing nitrocelluloses of about 11% nitrogen content, we have realized yields of high grade nitrated product of about 144% to 145%, based on the bone-dry weight of cellulose fiber used as a raw material. These yields are practically equal to those obtained when the liber is made into paper and disintegrated into small pieces before nitration. It is important that shredding be uniformly line, since otherwise the quality and yield of nitrocellulose product suffer. When, for instance, no attention is paid to the shredding operation, hard fiber clumps may be present in the shredded material. Upon nitrating the shredded material and dissolving in suitable solvents, hazy solutions are obtained. This haziness probably results from the presence of gelatinous products produced by hydrolysis of the fiber clumps.

If desired, the shredded fiber may be coated with reaction-retarding material such as waxes and oils, as described in our patent application hereinbefore referred to, as such material further improves the liber for nitration. Apparently such material, even when used in such amount to produce exceedingly thin coatings or films on the fibers, protects them from gelatinization and hydrolysis during nitratlon. Preferably, the reaction-retarding material employed is free from objectionable color-yielding or stabil- .ity-lowering mattenparaffin oil, paraflin Wax, and stearic acid being examples of material of this type. These materials may be dispersed in Water containing small quantities of a soap such as potassium oleate as the dispering agent. The dispersion may be added to the pulp and the react-ion-retarding material fixed on the fibers through the use of, say, alum or other precipitatlng-agent. If the fiber has been stored in dry condition 10C and requires wetting, the dispersion may be f added to the water used for wetting the pulp i to the moisture content desired for shredding.

While our discoveries may be applied to advantage in conditioning cellulose fibers of various origins for conversion into nitrocelluloses, they have especial signilicance when applied to reiined `wood pulp of high alpha cellulose content, say, at least about 94%. Such wood pulps are highly absorptive as a result of removal of non-alpha cellulose impurities therefrom, and when prepared in luifed form, as ordinarily for nitration, they give disappointing results, probably because of the additive effect of the absorptivity of the individual fibers and the absorptivity of the mass. At the early stages of our research work, we were at a loss to account for lthese results, as one might expect good results from the desirable chemical composition of such fiber. By conditioning such fiber` as herein described, it is possible to realize the advantages to be expected from such wood fiber without incurring such expense as to nullify the economic advantage which such fiber now en]oys over'cotton.

e claim:

1. In the conditioning of cellulose pulp for conversion into cellulose derivatives, those steps which comprise shredding the pulp While wet and containing about 40% to bone-dry cellulose, and directly drying the shredded pulp from such condition.

Finely shredded cellulose pulp especially adapted for nitration and having the physical condition resulting from shredding the pulp While Wet and containing about 40% to 70% bone-dry cellulose and directly dried Jfrom such condition.

8. Finely shredded cellulose pulp treated with reaction-retarding material.

4. Finely shredded wood pulp of an alpha cellulose content of at least about 94% and having the physical condition resulting from shredding the pulp While wet.

'5. A dried, finely-shredded Wood pulp having that condition resulting from fine shredding of such pulp in bulk form while Wet and containing about 40%' to 70% bonedry pulp and directly dried from such condition.

6. In the preparation of nitrocellulose from a mass of cellulose pulp, those steps which comprise finely shredding the mass While it contains suiiicient moisture distributed therethrough so that its bone-dry cellulose content is about 40% to 70%, directly drying the shredded pulp from such condition, and directly nitrating the resulting dried and shredded pulp.

7. In the prepa-ration of nitrocellulose from a mass of dry, cellulose pulp, those steps which comprise incorporating sufficient moisture throughout the pulp to reduce its bonedry cellulose content to about 40% to 70%, finely shredding such pulp, directly drying the shredded pulp from such condition, and directly nitrating the resulting dried and shreddedpulp.

8. A process which comprises dewatering an aqueous suspension of cellulose pulp to a bone-dry cellulose content of about 40% to 70%, nely shredding the pulp in such condition, directly drying the shredded pulp Jfrom such condition, and directlynitrating the resulting dried and shredded pulp.

9. In the preparation of nitrocellulose from a mass of cellulose pulp, those steps Which comprise coating the pulp fibers with reaction-retarding material, finely shredding the mass While it contains suicient moisture distributed therethrough so that its bone-dry cellulose content is about 40% to 70%', drying the shredded pulp, and nitrating.

10. In the preparation of nitrocellulose from a mass of dry cellulose pulp, those steps Which comprise treating the pulp with an aqueous dispersion of` reaction-retardingl material to coat the pulp fibers with such material and to associate suihcient moisture therewith to reduce its bone-dry cellulose content toabout 40% to 70%, inelyshredding the pulp, drying the shredded pulp, and nitrating.

11. Dry, nelyshredded Wood pulp of high alpha cellulose content substantially free from hard liber clumps and ber dust.

12. Dry, finely shredded Wood pulp of an alpha cellulose content of at least about 94% signatures.

MILTON O. SOEUR. BNENJAMIN G. HS. 

